I have found that (since updating to Keyshot 7) when I delete a Part from a Group within the model tree, the Hide/Show toggle button for the Group becomes disabled. Generally I just have to right click, then go to the Visibility menu to get it back, but it's a bit of a pain.
Windows 10
KeyShot version: 7.3
Rhino 5
Steps to reproduce:
Import 3DM into Keyshot from Rhino - delete a part from any group, use the hide button in the model tree, try to toggle button back on to show the group (doesn't work, remains hidden)